Kip Kinkel -- who murdered his parents before opening fire at Springfield's Thurston High School in 1998, killing two and wounding 25 -- also collected guns and spoke openly about plans to use them.

Between Oregon's two worst mass shootings, at least four other attackers opened random fire at an Oregon school, mall or other public setting.

Still, experts said, a lot has changed since Thurston -- and Columbine, the following year -- seared "school shooting" into the nation's consciousness. Authorities may be no closer to predicting when a troubled soul will tumble into violent madness, but they've made strides in identifying those on the edge and nudging them back.

"You're not going to be able to look at someone and say, 'Two years from now, he's going to be the next school shooter,'" said Mario Scalora, a psychologist at the University of Nebraska-Lincoln who consults nationally on how to thwart mass shootings and other targeted violence.

But Scalora and others said listening -- and speaking up when something isn't right -- can stop such crimes. A burgeoning field of study called risk assessment is also making a difference.

Mass shootings "are very preventable," Scalora said. "In a lot of cases, there are warning signs."

He added: "It's the non-mentally-ill people who hear these things and don't make an effort to reach out and say, 'This guy needs help.' If we want to make a difference, that's where we can."

*

Dozens of mass shootings have unfolded in the U.S. since 1966, when a former Marine shot 45 people from a University of Texas tower, killing nearly a third of them.

Experts have learned that those willing to fire guns at strangers usually share traits: Almost all are men. Many -- but not all -- are white, middle class and 20 to 40 years old. They tend to be loners or hang with other self-styled outcasts. They typically come from tumultuous families, nurse grievances and have a mental illness.

The problem, experts warn, is lots of people fit this profile. Most lonely young white men will never go on to commit violence -- and people who struggle with mental illness are far more likely to be the victim of violence than a perpetrator.

The traits "don't differentiate shooters from everyone else in the country who's lonely, " said Peter Langman, a forensic psychologist who has studied school shootings for 15 years.

"We can't lock them all up," agreed Tony Farrenkopf, a Portland-based forensic psychologist who studies shooter profiles. "We'd lock up a lot of people who won't do anything."

So experts pay attention to the profile but take it a step further. The ones who go on to kill, they say, also collect weapons -- from bomb parts to bullets and guns. And they tend to talk about their plans and leave other clues. Sometimes a lot of clues.

Months before he opened fire in Thurston's cafeteria, the 15-year-old told a friend on the school bus how he'd bring guns to school one day and shoot classmates. He also wrote about murder in class assignments.

A student who overheard the conversation regretted not reporting it.

"I should have. I know I should have. But I didn't," he told The Oregonian days after the shooting. "The way him and (his friend) were talking about it, it seemed like a joke, like they were planning a video game."

The gunman who killed 12 and wounded 70 at a Colorado movie theater in 2012 told a psychiatrist well before the attack that academic struggles had left him grappling with homicidal urges. The threats made their way to University of Colorado police officers, but they did little.

A failing student at the University of Arizona warned more than a year before he shot three professors dead in a lecture hall in 2002 that he "might put something under the college."

"Whatever has gotten them to the school, through the doors, has been with them for a while," said Frank Farley, a psychologist at Temple University.

The Roseburg shooter's red flags, at least the ones known so far, weren't as glaring. But experts say they were still in plain sight.

He wistfully posted on his blog about the infamy earned by another shooter this year -- the former TV reporter who gunned down two ex-colleagues on live TV. And though he struggled with mental illness, his mother encouraged him to add to his arsenal.

Palarea, an operational psychologist who consults for the U.S. State Department and private corporations, works in a field that has flourished since 2000: threat assessment.

The work links professionals in mental health, education, juvenile justice and law enforcement, and involves art as much as science.

Investigators accustomed to tracing crimes may struggle with the shift to examining crimes that may never happen. But once they get it, experts say, it works. In 2014, an FBI official told The Associated Press that threat-assessment teams had foiled nearly 150 plots that year.

Once a potential shooter is flagged -- maybe someone saw him posting threats on the Internet -- assessment teams scramble to calculate the risk:

Does the person have a mental illness or anger-control issues? What about a history of escalating violence? Does he have friends? Does he get along with relatives? Does he have easy access to weapons? Has some event -- such as a job loss or breakup -- pushed him to the brink?

Depending on the answers, threat-assessment teams can work with mental health authorities and courts to take any guns away. They might see about committing the potential shooter to a mental health facility. They'll offer counseling or tutoring. Friends, relatives, co-workers and others are drafted to help keep the person on track and to flag any warning signs.

Sometimes that's all the person needs. Other times, that's not enough.

In 2002, for example, officials in the Salem-Keizer School District thought they had helped a McNary High School student through a dark chapter, according to a story this month in Mother Jones magazine. Salem boasts one of the best-known risk assessment operations in the nation -- with its members asked to train educators and cops around the country.

Erik Ayala, as a 16-year-old junior in 2000, told someone he wanted to bring a gun to school to shoot "preps." He was hospitalized after a suicide attempt and then given a "wraparound intervention," with treatment, tutoring and attention from friends. Ayala was among the first students handled by the district's assessment team, which launched the same year.

But in 2009, after Ayala moved to Portland, the gloom returned. He was broke. He couldn't get a girlfriend. He bought a handgun and opened fire on teenagers waiting to get into an all-ages nightclub called The Zone. Two girls died. Seven people were hurt.

"We spend a lot of time nudging people off the path they're on and orchestrating social connections and meaningful experiences," said John Van Dreal, Salem-Keizer's school psychologist. "Later in life, he lost access to that."

Van Dreal said the more communities and police agencies around the country embrace threat assessment, "the more that can be done for people like Erik. People will be more aware."

Amoroso denied he was a danger, despite being found outside the stadium with a loaded gun, ammunition, binoculars and a book about a stadium sniper attack. When police searched his home, they found more guns, more bullets, sniper gear, a bulletproof vest and a piece of steel that had been shot with an armor-piercing round. Amoroso also had a history of making threats and harming people -- findings uncovered in a threat assessment.

A judge sentenced him to three years in prison on gun charges and ordered counseling. Amoroso is now under post-release supervision.

"He is intelligent enough to be able to follow societal rules when it suits him," prosecutors wrote in a sentencing memo that asked for seven years, "but his history and recent conduct show he is very disturbed."

A clerk at the Grants Pass public safety department confirmed that officials were notified when Amoroso was released. Deputy Chief Jim Hamilton didn't return messages seeking comment on whether Amoroso is still in Grants Pass or whether someone is keeping tabs on him.

"You never close a case. You never shred a file," said Palarea, the risk-assessment psychologist. "There are some folks, even when you get them through one situation, they present a threat again."

Palarea knows that's not easy: "Law enforcement resources are not limitless." Others worry that risk assessment could grow to encroach on civil rights.

"Even if you get to prediction, should we do preventive detention?" asked Farley, the Temple psychologist. "Very few people are advocating for that -- even if we could predict who will kill whom."

Scalora, the Nebraska psychologist, said agencies across jurisdictions must remain linked. And the rest of us must pay attention. Experts say that means they'll have to work harder at teaching loved ones, classmates -- everyone -- how to spot and report warning signs.

"How do you get people to come forward," Scalora said, "when they have a concern?"

*

The Internet and the rise of social media have made it easier for authorities and others to flag disturbing statements from someone ready to kill. But experts worry they're also fueling shootings.

Wikipedia pages and online news archives preserve killers' legacies years after headlines fade, giving copycats a recipe for murder and notoriety. Shooters, seeking maximum damage and infamy, may shun a venue connected to their grievance in favor of a mall or other public place.

"This is where you start to see notoriety and attention-seeking becoming a motive," Palarea said. "It's easier than ever for people to make their mark and have their name noted in history."